The present invention relates to an optical disk apparatus and, more particularly, to an optical disk apparatus for performing tracking by detecting prepits or a pregroove or pregrooves.
An optical disk apparatus can record data at high density and is widely used for recording a large amount of data such as image data. An optical disk used in the optical disk apparatus has tracks such as prepits, a pregroove or the like formed in a spiral or concentric form. A laser beam irradiates the optical disk rotating at a high speed. In the recording mode, while a low level laser beam tracks the prepits, a high level laser beam selectively irradiates the disk to form data pits in accordance with recording data, thereby recording the data. In the reproducing mode, the data pits are traced by a reproduction laser beam, thereby reproducing the recorded data.
In the optical disk apparatus described above, a laser beam is focused by an objective lens on a track of a narrow width of about 1 .mu.m which is formed on an optical disk. However, the laser beam must be quickly positioned at the target track for satisfactory tracking. Therefore, tracking control is generally performed. When an optical disk is damaged, when dust attaches to it, when a pregroove is partially absent, or when an external vibration is applied thereon, a tracking error occurs in the tracking control. In other words, the laser beam is deflected from the target track and then "jumps" to another track. When such a tracking jump occurs, data cannot be correctly recorded and reproduced.